1. Field
This disclosure relates to signal processing.
2. Background
Image information captured by image capture devices, such as digital still photo cameras, may be susceptible to noise as a result of physical limitations of the image sensors, interference from illumination sources, and the like. With the increased demand for smaller image capture devices, e.g., in multi-purpose mobile devices such as mobile wireless communication devices, comes the need for more compact image sensor modules. The decrease in the size of image sensor modules typically results in a significant increase in the amount of noise captured within the image information.
Image quality may vary greatly among different model lines of cellular telephone (“cellphone”) cameras and other inexpensive digital cameras. Unlike the models of a line of conventional digital cameras, different models of cellular telephones may have different optics and different sensors. Variations between high-quality optical systems of conventional cameras are typically much less than variations between the optical systems of cellphone cameras, which may be made of glass or plastic, may or may not include one or more optical coatings, and may have very different resolving powers. Similarly, the various models of a line of conventional digital cameras typically have the same sensor, possibly in different sizes, while cellphone cameras of the same line or even the same model may have very different sensors. As a result, images from different models of cellphone cameras will typically be much more different from one another than images from different models of conventional cameras.
In order to produce commercially acceptable image quality from a cellphone camera or other inexpensive digital camera, it may be desirable to perform a filtering operation (also called a “post-processing procedure”) on the captured image. Such an operation may be designed to enhance image quality by, for example, reducing artifacts and/or increasing edge sharpness. The process of determining an appropriate post-processing procedure for a particular camera is also called “camera tuning.” Typically, camera tuning is repeated whenever a new lens and/or sensor is used.